1. Field of the Invention
The present invention relates to a pneumatic tire such as a studless tire that is suitable for running on snowy and icy road surfaces.
2. Description of the Prior Art
For improving the running performance on snowy and icy road surfaces of pneumatic tires, it has been considered, in the prior art, that it is effective to partition tread portions into blocks and to provide a large number of sipes in those blocks for increasing edge effects thereof. On the other hand, accompanying an increase in the number of provided sipes, large collapsing of blocks is apt to occur as illustrated in FIG. 6(B). The applicant has thus suggested in Japanese Patent Laid-Open Publication No. 2003-25812 sipes having a configuration in a so-called Miura-Ori fold for preventing such excessive collapsing of blocks.
Such sipes have a configuration in a plane parallel with the block surface that comprises a zigzag part extending in the length direction of the sipes. Such zigzag parts displace upon being turned back to one side and to the other side in the length direction of the sipes in the course the sipes reach from an open top end that opens at the block surface to a bottom thereof. Such sipes are arranged in that mutually opposing sipe surfaces comprise three-dimensional concaves and convexes, wherein these concaves and convexes are in mesh with each other. With this arrangement, block pieces among sipes will become integral with each other so as to improve the block rigidity, and it is accordingly possible to prevent excess collapsing of the blocks.
However, it was further found that, for the purpose of further improving the rigidity of the entire block or the edge effects thereof, it is necessary to improve a plurality of sipes included in the blocks in a mutually correlated manner, in addition to improving configurations of each sipe.
The present invention has been made in view of such problems, and it is an object thereof to provide a pneumatic tire that is capable of further restricting collapsing of blocks and of further improving the running performance on snowy and icy road surfaces on the basis of an arrangement in which first sipes and second sipes of different positions of turn-back points of displacement are included in at least one block.